Production of photographic images making use of the intensity-reversal effect



United States Patent 3,156,564 IRGDUCTION 0F PHQTOGRAPHHZ IMAGES .MAKENG USE OF THE EWTENSHY-REWR- SAL EFFECT Ren von Warthurg, Basel, Switzerland, assignor to .lohu Eggert, Zollilron, Zurich, Switzerland N0 Drawing. Filed Mar. 4, i959, E'Ser. No. 797,056 Claims priority, application Switzerland Mar. 11, 1958 9 Claims. (Cl. 96-45) The present invention relates to materials and processes for the production of photographic images by means of silver halide emulsions having intensity-reversal effect susceptibility. More especially, the invention relates to the production of screened and non-screened direct positive images and to the production of compensated or tonevalue corrected cop'es from negatives having a large image density range. According to a preferred feature of the invention, these processes are carried out by means of special silver halide emulsions which contain silver iodide and are subjected to a physical ripening in the presence of at least one inhibitor andwhich are not subjected to chemical ripening.

It is an old problem to produce direct duplicates from given originals by photographic methods. The reversal process is normally used for this purpose either by contact printing or by photographing the original with a camera. It is possible in this way to operate with a small exposure, but it is always necessary to use a particular photographic reversal development method that requires the use of several successive baths. In order to achieve the same object of producing direct duplicates, it is possible to use diazotype or allied processes, for example, electrostatic methods. However, in all these cases, apart from special materials and development methods, it is necessary to have special equipment and a comparatively long exposure. The same applies to diffusion transfer processes which, although they require smaller exposure, necessitate the use of two different types of photographic layers. Finally, it is possible for the'same purpose to use certain photographic effects in which the reversal is obtained by a second exposure, such as solarization, the Clayden eifect, Sabattier effect or Herschel eilect. A long exposure is however also necessary in these cases. Also included herein is the intensity reversal effect, observed by R. W. Wood in 1901, later reported in the work by H. Arens in Zeitschrift fiir v-Jissenschattliche Photographic, vol. 32, page 237 (1934), and also by R. E. Maurer and J. A. C. Yule in the Journal of the Optical Society of America, page 402 (1952), referred to therein as low-intensity desensitization. The intensity reversal effect consists in that, with a layer subjected to brief initial exposure with a high light intensity, the latent image completely or partially loses its capacity for chemical development when the layer is after-exposed for a long period with low light intensity. It is clear from the aforesaid literature references that the intensity reversal ei ect occurs in more or less pronounced form with different (high sensitive and low sensitive) layers and can be used for practical purposes. However, the works reference to above do not disclose the special layer and exposure conditions which lead to a reproducible intensity-reversal effect and which can be used. in practice.

According to the present invention direct positive images with improved photographic properties are produced while making use of the intensity-reversal effect by means of a silver halide emulsion containing silve iodide, preferably silver iodo bromide emulsion, which is subjected to physical or Ostwald ripening in the presence of at least one photographic .inhibitor'or stabilizer and which has not received a chemical ripening.

" The silversalt of'said emulsion preferably consists of I 3,156,564 Patented Nov. 10, 1964 0.1-50 mol percent of silver iodide and 99.9-50 percent of silver bromide, whereby amounts of 0.1-12 mol percent of silver iodide have proved to be especially advantageous. The silver bromide of said emulsion may be partially re placed by silver chloride. The physical ripening of the emulsion is preferably performed in the presence of a surplus of water-soluble bromides, especially potassium bromide, whereby a surplus of 5-400, especially 5-200, mol percent of bromides over the theoretical amount has proved to be especially advantageous. It is furthermore possible to use besides silver salts small amounts of other heavy metal salts such as, for instance, thallium salts, in the preparation of the present emulsions.

As inhibitors there come into question the well-known substances which are used in the photographic art as ripening retarders in the production of silver halide emulsions, as stabilizers for increasing the stability of silver halide emulsion layers, or as anti-fogging additives to silver halide developers. Preferred inhibitors are the 1,3, 4-triazaindolizines, especially the 7-hydroxy-1,3,4-triazaindolizines, as they are, for instance, disclosed in United States Patents Nos. 2,444,605; 2,444,606 and 2,449,225. In this connection there may also be mentioned the 7-hydroxy-1,3,4-triazaindolizines which are substituted in the 6-position by a halogen atom especially by chlorine or bromine. Further suitable inhibitors are, for instance, benzotriazole (lH-benzotriazole or 1,2,3-benzotriazole), methylbenzotriazole, o-nitrobenzotriazole, histidene, ethylbenzoxazole, N-ethylpyrrole and 2,3-dimethylquinoxmine (2,3-dimethyl-l,4-benzodiazine). The inhibitors are generally applied in amounts of about 0.01-1 g. per 100 g. of silver.

The precipitation of the silver salt is carried out at 40- (1., with gelatin or another suitable film-forming agent used as a protective colloid. As pointed out above, the precipitation of the silver salt is carried out in the presence of a molar surplus of a water-soluble bromide, especially potassium bromide, in order to achieve a physical ripening of the precipitated silver salts. It is furthermore possible to carry out the precipitation in the presence of ammonia.

After the precipitation and after the physical ripening has been achieved, the emulsions are Washed with Water, whereby the emulsions are adjusted to a volume conductivity of about 900-1600 international reciprocal ohmcentimeters. During the washing operation the inhibitor which is present in the emulsion is washed out at least partially. After the washing, the emulsion is not subjected to chemical ripening (chemical ripening isusually applied in the production of highly sensitive silver halide emulsions by subjecting the washed emulsions to a heattreatment in the presence of chemical sensitizers). It has proved advantageous to add to the present washed emulsions water-soluble bromides, as, for instance, potassium bromide, in amounts of 1-4 g. per liter of emulsion.

The photographic layer produced from these emulsions in well-known manner either on a paper, a film or a glass support, should have a high silver content as, for instance, 2-50 g. preferably 10-50 g. of silver per square meter.

A layer of the said type shows a pronounced intensityreversal effect. if such a layer is subjected to a diffused initial exposure with a burning period of 10* sec. and

The term printing as used herein and hereinafter refers to contact printing and also to enlargement or reduction by optical image formation.

Example 1 An emulsion having the following specification is prepared by use of the following four solutions:

I. Water ml.. 4000 Gelatin g 160 Potassium bromide g 500 Potassium iodide g 30 -methyl-7-hydroxy-1,3,4-triazaindolizine g 0.9

II. Water ml 2200 Silver nitrate g 200 III. Water ml 2200 Silver nitrate g 200 IV. Gelatin g 400 Water rnl 1500 Solution I is kept at 70 C. and solution 11 is run thereinto within one minute. After an interval of one minute, solution III is run in over a period of minutes, during which time a physical ripening of the resulting silver bromide-silver iodide mixture is produced. After completing the precipitation, the solution of swelled gelatin (IV) is added and the mixture is immediately cooled. After solidifying, the emulsion is washed with water as indicated above. For casting purposes, 3.5 g. of potassium bromide are added per 1000 ml. of emulsion. The 5-methyl-7-hydroxy-l,3,4-triazaindolizine solution I is an inhibitor for preventing chemical ripening.

For the brief initial exposure of the layer produced from said emulsion, an electronic flash-lamp is employed. The intensity of the initial exposure depends on the desired density of the final image and on the sensitivity of the direct duplicate material. The initial exposure can be obtained with a single electronic flash exposure or by a relatively large number of electronc flash exposures of lower intensity. There may, for instance, be used an electronic flash lamp having a discharge energy of to 50 watt-seconds and a discharge time of lO to 10 sec. at a distance of 60 cm. from the layer. if there is used a photographic film having a silver halide layer with a thickness of 20 microns, there may be obtained a maximum density of 4 after development of the exposed layer with an ordinary silver halide developer. The layer thus initially exposed can now be exposed in contact with the printing original or in a camera, the exposure advantageously being effected through a mirror in order to obtain an image which is not laterally reversed. The slow exposure, which is in principle to be at least 100 times longer than the initial exposure, is so chosen that subsequently an image of the desired density distribution is formed. For instance, exposures which are 10 to 10 and preferably 10 to 10 times longer than the initial exposure. If the exposure is made in the camera, an original is, for instance, exposed with 4 carbon-arc lamps a distance of 1 meter, said lamps being arranged an angle of about 45. If the aperture or diaphragm stop of the camera is adjusted to f/ 11 (U.S. No. 8), the exposure time amounts to 10 to 20 seconds. The layer is then developed with a conventional developer, whereupon it is fixed in the usual way with an acid fixing bath, and thereafter rinsed and dried. The result is a direct duplicate of the original.

As a developer there may, for instance, be used a solution of the following composition:

Water up to 1000 cc.

Example 2 An emulsion is prepared as described in Example 1 and this emulsion is subjected in liquid form in a layer of thickness of for example 0.1 mm. either to a single brief initial exposure of high light intensity or to several brief initial exposures of lower intensity, if desired by allowing the emulsion to flow between two light-pervious plates suitably spaced apart during the exposure to light. Thereafter, the initially exposed emulsion is cast on to the final layer support. After drying, the slow exposure for forming the image is carried out as indicated in Example 1. Conventional photographic processing then provides a direct duplicate of the original.

Example 3 An emulsion is prepared as described in Example 1 and this is cast in a layer of thickness of for example 0.2 mm. on to a support, for example a conveyor belt. After the layer has solidified, this is subjected either to a single brief initial exposure with light of high intensity or to several brief initial exposures with light of lower intensity. Thereafter, the layer is again melted and cast on to the final layer support. After drying, the slow exposure for forming the image is carried out as indicated in Example 1. Usual photographic development also provides a direct duplicate of the original in this case.

According to the present invention, the intensityreversal effect may also be used for the production of screened duplicates from continuous tone originals.

When reproducing continuous tone images, the usual procedure is for the original to be processed to give a screened exposure or print by using a screen in a camera or in contact. This process presupposes the use of a screen or raster. Consequently the practice has frequently been adopted of using special prescreened photographic materials for the exposure or print. Such materials have a different light-sensitivity at different areas, this sensitivity showing a continuous increase and decrease according to the screen spacing. If any desired original is printed in the camera or by a contact process on to such a material, a screened or lined image is formed after the normal processing thereof, the tone values of this image being opposite to those of the original.

It has now been found that layers of similar type can be produced, but with the difference that the screened image formed after normal processing has tone values which are parallel with those of the original. In this case, therefore, with the exposure made in the camera or with the contact print, a screened direct duplicate of the original is produced. The procedure followed according to the invention is that a screen is first of all printed by brief exposure with light of high intensity on to a photographic material of steep intensity and showing a pronounced intensity-reversal effect, and thereafter the original to be screened is printed thereon by relatively long exposure with light of weak intensity, whereafter the material is developed in the usual way and thus a screened direct duplicate of the original is obtained.

As shown above, the intensity-reversal effect can be used for the production of direct duplicates by the first brief exposure to light being so diffused over the entire layer that without subsequent exposure, the maximum density of the layer could be developed. The subsequent slow exposure is thereafter carried out to form an image. In the development, a duplicate of the exposed original is obtained. In the present case, the process is modified, in that the brief initial exposure is not diffused, but is made through a raster or screen. As a screen, it is either possible to use a half-tone screen in contact with the layer or a lined screen at a suitable spacing from the layer. The exposure is so chosen that also at the areas at which the layer receives the smallest light quantities, the layer would be completely blackened by an immediate development. Dut to the fact that the layer has experienced a varying initial exposure, according to the scale of the screen it also has a positive sensitivity distributed in the manner of a screen. If the positive density curve of the type of layer employed is sufficiently strong, a screen duplicate of the original is consequently formed when an original is exposed and thereafter developed. For carrying through this process there are advantageously used the emulsions disclosed hereinbefore.

Example 4 A layer having a strong intensity-reversal effect and a steep gradation of the slow exposure, of for example 7: 10, is briefly exposed to light behind a contact screen by means of an electronic flash lamp, i.e., for a period of maximum duration of 10- sec. with high intensity light. The exposure to light takes place for example at a distance of 60 cm. with a light having a discharge energy of 50 watt-seconds. Instead of using this single exposure, it is also possible to make several brief exposures with light of lower intensity. The layer thus prepared is used in a reproduction camera. When photographing a continuous tone original in the scale of 1:2, an exposure time of 20 seconds is necessary'for the slow exposure which takes at least 100 times longer than the flash exposure, this exposure being made with illumination from a low light intensity using four are lamps, each of 30 amperes at a distance of 1 meter, and a diaphragm stop of f/ 22, in order to obtain a correctly screened duplicate of the original after development has taken place in the usual way. The layer used for performing this process may be produced from the emulsion disclosed in Example 1.

As stated hereinbefore, the process of the present invention may also be used for the production of compensated copies from negatives which have a large image density range, whereby especially adavantageous results are obtained with the speical emulsions disclosed hereinbefore.

It is a known problem to produce copies of negatives having extremely large image density ranges by photographic methods. The normal copying or printing technique does not give satisfactory results, for even on soft printing layers, such a negative yields a copy which certainly portrays the highlights in detail, but contains sooty shadows with poor detail, or on the other hand gives a print which shows the shadow portions satisfactorily, but which has chalky highlights without detail. In order to overcome this difficulty, masking processes have been devised which enable the image density range of the negative to be reduced. Included in this category are also the tone-separation processes, in which the gradation of the printing. material is so adjusted that the richness in detail of highlights and shadows can be emphasized at the expense of the details in the medium tones. Electronic methods have also been used for the purpose of so controlling the intensity of the printing light be tween image elements that a continuous compensation in the copy of all the details from the highlights to the shadows is obtained.

With all these processes, additional expense must be incurred for solving the problem in question, either by producing individual masks, by making use of special printing materials or photographic operations suitable therefor, or even by using complicated and costly electronic means.

It has now been found that compensated prints from negatives (or positives) having a large image density range can be produced more easily by means of a silver halide emulsion layer having pronounced intensity-reversal effect susceptibility, whereby printing .is carried through in such a way that withthe short time exposure an image of the negative is sharply or distinctlyformed and withthe longtime exposure an image of the negative is blurred or indistinctly formed. In carrying through this process, two contrasting photographic processes are combined, one process being an image-forming process in which an image of the negative is sharply formed, and the other being a compensating or desensitizing process in which an image of the negative is indistinctly formed. After the exposure, the layers are developed in the usual way.

In any case, the silver halide emulsion layer is exposed to the image to be reproduced in focus with said image when exposing said layer with the high intensity light and the layer is exposed to said image slightly out of focus with said image with the low intensity light, and at the same magnification as the first mentioned exposure.

The high intensity exposure can be carried out first of all as the image-formingoperation, this being followed by the low intensity exposure for the compensating operation. However, it is also possible to operate in the reverse sequence.

By the sharp printing of the negative with a large image density range on to the printing material, which preferably is as hard as possible (gamma preferably higher than 3), a copy which has steep total gradation and a steep gradation of the image detail is formed. The total or overall gradation is reduced by the subsequent degradating exposure or by the preceding desensitizing exposure to the desired value by a suitable choice of the exposure, while owing to the lack of sharpness of this compensating exposure, the steep gradation of detail obtained in the image-forming exposure is maintained. The combination of both types of exposure thus yields the desired compensated print.

Example 5 on to the paper and the synthesizing brief exposure is made. For this purpose, with an enlargement of 2 and a diaphragm stop of f/5.6, it is for example necessary to use a flash energy of 1,000 watt-seconds. After this exposure, the paper is covered with a sheet of opal glass. By means of the continuous light, a second slow degradating exposure is now carried out. The necessary lack of sharpness or blurring is produced by the opal glass. When using a 150 watt cold light lamp, an exposure time of for example seconds is necessary under the conditions described above. The photographic material is thereafter developed and fixed in the usual way. The result is the desired compensated print.

Example 6 A compensated print such as that of Example 2 can also be obtained with the same arrangement and by using the same type of layer if the sequence of the two exposures is reversed. By means of the first slow and non sharp exposure, the layer is image-wise desensitized. The synthesizing brief and sharp exposure is then carried out by means of an electronic flash. Using the same layer and the same arrangement as in Example 2, the procedure for the enlargement is the same, except that the sequence of the exposures is reversed and the previous slow exposure is now for example extended to 30 minutes.

What I claim is:

1. In the process of producing a direct positive photographic reproduction with a photographic emulsion that is subjected to intensity-reversal by an intense diffuse flash exposure of not more than 0.01 second, the improvement according to which the emulsion used is one which has been subjected to a grain size ripening while containing an anti-fogging agent, and has not been subjected to a chemical ripening.

2. The combination of claim 1 in which the emulsion is a silver iodobromide emulsion.

3. The combination of claim 1 in which the emulsion is a silver halide emulsion and from 0.01 to 50 mol percent of the silver halide is silver iodide.

4. The combination of claim 1 in which the emulsion is subjected to the flash exposure before it is cast into an image-receiving layer, and is subjected to a photographic image after it is cast into such layer.

5. The combination of claim 1 in which the flash exposure is performed through a screen to print the screen on the emulsion so that a screened direct positive print of the subject to be produced is obtained.

6. The combination of claim 1 in which the flash exposure is a focused imagewise exposure and the second exposure to light of lower intensity is a blurred imagewise exposure.

7. The combination of claim 1 in which the anti-fogging agent is a 1,3,4-triazaindolizine.

8. The combination of claim 1 in which the anti-fogging agent is selected from the class consisting of hemetriazole, methylbenzotriazole, 6-nitrobenzothiazole, histidine, ethylbenzoxazole, n-ethylpyrrole and 2,3-dimethylquinoxaline.

9. The combination of claim 1 in which during the grain size ripening the anti-fogging agent was present in an amount between 0.01 and 1 gram per 100 grams of silver.

References Cited in the file of this patent UNITED STATES PATENTS 2,401,051 Crouse et a1 May 28, 1946 2,444,605 Heimbach. et al July 6, 1948 2,691,585 Yule et al. Oct. 12, 1954 2,691,586 Yule et al Oct. 12, 1954 2,708,626 Yule et al May 17, 1955 2,912,326 Maurer Nov. 10, 1959 2,912,328 Maurer Nov. 10, 1959 3,000,739 Mafiet Sept. 19, 1961 OTHER REFERENCES 

1. IN THE PROCESS OF PRODUCING A DIRECT POSITIVE PHOTOGRAPHIC REPRODUCTION WITH A PHOTOGRAPHIC EMULSION THAT IS SUBJECTED TO INTENSITY-REVERSAL BY AN INTENSE DIFFUSE FLASH EXPOSURE OF NOT MORE THAN 0.01 SECOND, THE IMPROVEMENT ACCORDING TO WHICH THE EMULSION USED IS ONE WHICH HAS BEEN SUBJECTED TO A GRAIN SIZE RIPENING WHILE CONTAINING AN ANTI-FOGGING AGENT, AND HAS NOT BEEN SUBJECTED TO A CHEMICAL RIPENING. 